impossible to filter it from the interstellar hydrogen noise.This is something I did not know. What should I make of the SETI project then? totally hopeless?
Also, do you think Carl Sagan was unaware of this when he wrote 'Contact'? the plot premise is that a machine in orbit around Vega receives pretty much the earliest radio broadcast powerful enough to escape the ionosphere.
He had another idea on how to say 'I'm here' - to seed a star with a huge amount of rare metals to give it a totally unnature absorption spectrum. Probably even more impossible, though.